The broad, long-term objective of this proposal is to identify new effective strategies for blocking the angiogenesis that contributes to the pathology of cancers and other important disorders. Specific Aim 1 is: Identify key signaling pathways through which collagen I and the alpha1beta1 and alpha2beta1 integrins drive the assembly of endothelial cells (ECs) into capillary structures in vitro, and test key signa!ing molecules as targets for inhibition of angiogenesis driven by vascular endothelial growth factor (VEGF) in vivo. Specific Aim 2 is: Define the importance of alpha6 integrins for VEGF-driven angiogenesis. The cumulative evidence suggests the hypothesis that the alpha1beta1 and alpha2beta1 integrins serve pivotal functions in regulating the EC cytoskeleton and thereby in driving EC assembly into capillary structures. Thus, Aim 1 is designed to define key signaling pathways and effectors through which collagen I ligation of the alpha1beta1 and alpha2beta1 integrins regulates the formation of capillary structures in vitro. The significance of identified effector molecules for VEGF-driven angiogenesis in vivo will be established with a highly versatile athymic nude mouse model involving continuous expression of retrovirus encoding dominant-negative mutants. Aim 2 is designed to test the hypothesis, supported by our recent findings, that alpha6 integrins function importantly during VEGF-driven angiogenesis by activating signal transduction pathways critical for EC survival. Experiments with nude mice will define potency alpha6 integrin antagonism for inhibition of angiogenesis in vivo, alone and in combination with antagonism of alpha1beta1 and alpha2beta1 integrins, to determine if antagonism of each in combination provides cumulative inhibition of angiogenesis, as predicted by our prior work. Experiments in vitro will define specific signaling mechanisms through which ligation of alpha6 integrins supports survival of ECs. Thus, the experimental plan is designed to establish previously unrecognized and important functions for alpha1beta1 and alpha2beta1 and alpha6 integrins in angiogenesis, to define key signaling pathways through Which these functions are mediated, and to identify novel rational approaches for inhibition of pathological angiogenesis.